Mechanism for oscillatory assembly of microtubules.
Dampened oscillations of microtubule assembly can accompany polymerization at high tubulin subunit concentrations. This presumably results from a synchronization of dynamic instability behavior, which generates a large population of rapidly disassembling microtubules, that liberate tubulin-GDP oligomers. Subunits in oligomers cannot assemble until they dissociate, to allow GDP-GTP exchange. To determine whether rapidly disassembling microtubules generate oligomers directly, we measured the rate of dilution-induced disassembly of tubulin-GDP microtubules and the rate of dissociation of GDP from the so-formed tubulin-GDP subunits. The rate of GDP dissociation from liberated subunits was found to correspond to that of tubulin-GDP subunits (t1/2 = 5 s), rather than tubulin-GDP oligomers. This indicates that tubulin-GDP subunits are released from microtubules undergoing rapid disassembly. Oligomers apparently form in a side reaction from the high concentration of tubulin-GDP subunits liberated from the synchronously disassembling microtubule population. The rate of subunit dissociation is 0.11 s-1 with oligomers formed by concentrating tubulin-GDP subunits and 0.045 s-1 with oligomers formed by cold-induced microtubule disassembly. This difference provides evidence that the conformation of tubulin-GDP subunits released from rapidly disassembling microtubules differs from tubulin-GDP subunits that were not recently in the microtubule lattice.
Caplow
M
M
Department of Biochemistry, University of North Carolina, Chapel Hill 27599-7260.
Shanks
J
J
D000818:Animals; D001921:Brain; D002417:Cattle; D006153:Guanosine Diphosphate / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D066298:In Vitro Techniques; D007700:Kinetics; D008870:Microtubules / Q000502:physiology*; D008970:Molecular Weight; D010507:Periodicity; D011485:Protein Binding; D014404:Tubulin / Q000502:physiology*
D014404:Tubulin; D006153:Guanosine Diphosphate; D006160:Guanosine Triphosphate